Method and arrangement for the single-stage continuous production of a rubber base compound and a rubber end compound

ABSTRACT

The invention is directed to a method and an arrangement continuously producing a rubber base compound and a rubber end compound in a single stage for vehicle tires, drive belts, conveyor belts as well as for industrial rubber products. The rubber base compound and the rubber end compound are produced continuously in one and the same mixing arrangement which includes a twin-screw extruder.

FIELD OF THE INVENTION

The invention relates to a method and an arrangement for thesingle-stage, continuous production of a rubber base compound and arubber end compound for vehicle tires, drive belts, conveyor belts aswell as industrial rubber products.

BACKGROUND OF THE INVENTION

Rubber compounds which constitute the starting material of eachelastomeric product such as tires, conveyor belts, seals, elasticbellows and the like are complex reactive multicomponent systems whichgenerally comprise rubber, processing (softener) oil to stretch thepolymer and to improve the processing characteristics, chemicals forobtaining special characteristics such as fire protection and lightprotection, bonding agents, reinforcing filler substances such as soot,silicic acid or fibers for increasing the mechanical strength, andvulcanizing systems comprising vulcanizing agents, activators,accelerators and retarders.

Because of the different forms (lumps, granular material, powder,liquid), the extremely different viscosities and the very considerablydifferent parts by weight (for example, one part sulfur to 100 partsrubber), the mixing of these individual substance components constitutesa method and machine task which is most difficult. In addition, aspecial significance is imparted to the process for producing thecompounds since the physical and chemical characteristics of anelastomeric manufactured product are not only dependent upon theformulation of the rubber compound but also on the compoundingtechnology. Accordingly, the sequence of metering of rubber, soot andsoftener has a considerable influence on the soot dispersion andtherefore on the mechanical strength of the manufactured part.

According to the present state of the art, rubber compounds are almostexclusively produced in closed mixers characterized as masticators.

A closed mixer assembly comprises a metering system, weighing system andtransport system as well as the closed mixer, an extruder or rollerassembly for converting the charge of the closed mixer to rubber sheets,a refrigerating unit for the sheets and a positioning or cutting device.

The actual compounding process takes place in a chamber having twoclosable openings and two rotors rotating in mutually oppositedirections which are arranged parallel and are equipped with masticatingelements. The walls of the compounding chamber, the rotors, the chargingram and the discharge saddle flap are temperature controlled bycirculating liquid. The substance components are supplied with anactuated ram via the feed shaft while liquids are injectable via nozzlesdirectly into the mixing chamber. The edges of the rotating masticatingblades define gaps in which the material is sheared and dispersed. Themasticating elements are so configured that the mixing charge isforcibly conveyed in the longitudinal and peripheral directions. Theflow division resulting from the laminar flow field and therearrangement cause a distributive mixing effect. At the end of a cycle,the mixing chamber is opened by pivoting the saddle flap and thecompounded piece is discharged by the conveying action of the rotors.

The holding time or cycle time required to obtain a homogeneous compoundis empirically determined for each formulation. The process iscontrolled to end when the pregiven values of the time, rotor torque,rotor revolutions, the temperature of the material being mixed or theenergy supplied are reached.

The energy supplied via the rotors is for the most part dissipated inthe highly viscous polymer mass. Because of the thermally unfavorablesurface/volume ratio of the mixing chamber, the dissipation heat canonly be transferred to a limited extent. The temperature increase of thematerial being mixed resulting therefrom forms the basis of one of themost serious disadvantages of the closed mixing process, namely: inorder to avoid a premature start of the temperature-dependentvulcanizing reaction, a rubber compound must generally be produced witha closed mixer in several steps. In the first step, all non-reactiveconstituents are mixed. In the case of high concentrations of a chargingsubstance and thermal instability of the polymers, several cycles can berequired already for this purpose.

The premix characterized as the base compound is cooled down fromapproximately 100° C. to 160° C. to 20° C. to 40° C. after beingdischarged from the closed mixer and thereafter supplied to the endcompound stage. There, the reactive vulcanizing chemicals are mixed intothe base compound likewise with a closed mixer with a temperature ofapproximately 80° C. to 120° C. not being permitted to be exceeded. Theend compound contains all constituents after this stage and is, in turn,cooled down to 20° C. to 40° C. In many cases, the end compound isstored in advance of further processing for 20 to 40 hours in order toraise the quality of the material being mixed to the required level viadiffusive material transport during this storage time.

The production of rubber compounds with closed mixers is burdened withtwo substantial disadvantages. On the one hand, a closed mixer canprincipally be driven only discontinuously. From this, an interruptionin the continuous manufacturing sequence results with organizational andlogistical problems. on the other hand, the danger is present offluctuations in quality because start-up effects occur with each cyclebecause of the intermittent operation.

Secondly, the temperature of the material being mixed is influenced onlywithin narrow limits and it is for this reason that the mixing processmust be carried out in several stages and, after each mixing stage, areshaping and cooling must take place. Because of the multiple stages,the following consequences occur: the mixing time is lengthened, a verylarge energy requirement has to be satisfied because of the repeatedplastication and cooling of the compound and the necessity arises ofproviding storage and transport capacities for the intermediatecompounds.

Because of these disadvantages of the closed mixer, the development ofalternate mixing apparatus was begun already in the 1960s. Thus, thetransfer mix extruder known, for example, from published German patentapplication DE-AS 11 42 839 was investigated as to its suitability as arubber mixer. The foregoing concerns a single-screw extruder wherein notonly the rotating screw but also the stationary cylinder has conveyancepaths. The material is transferred several times from the conveyingpaths of the screw into those of the cylinder and back whereby a goodmixing effect is obtained. However, because of thermal reasons, thecombination of the production of rubber base compounds and rubber endcompounds in a continuous process sequence and achieving this in onlyone mixing arrangement was not possible.

A twin-shaft machine known from published German patent applicationDE-AS 16 79 829 is likewise suited only for end mixing. A Farrelcontinuous mixer comprises essentially two shafts journalled at oppositeends and rotating in mutually opposite directions with the shafts beingconfigured as conveying screws in the input area and as masticatingblades in the output area. The holding time can be influenced via therotational speed of the shafts and a throttle in the output crosssection.

Furthermore, a single-shaft machine developed by Buss AG andcharacterized as a co-masticator has become known for producing rubbercompounds. In this single-shaft machine, the blades of the screws in theco-masticator are penetrated over the surface in a manner comparable toa pin extruder. During the rotation, these breakthroughs engagemasticating teeth fixed in the cylinder. To increase the mixing actionin the longitudinal direction, the shaft carries out an oscillatinglongitudinal movement with each rotation (Kautschuk und Gummi,Kunststoffe, 38th year, no. 2/85, pages 116 to 121).

Finally, a method and an arrangement for producing rubber compounds isknown from U.S. Pat. No. 5,011,291 wherein two closed mixers arearranged in series. The first closed mixer supplies the base compound ofthe rubber while the second closed mixer takes over the task of the endcompound. The second closed mixer is located directly below the mixerfor the rubber base compound so that the rubber base compound can beguided directly into the finish mixer as a charge and can be furtherprocessed there.

It is true that with this method procedure the very costly cooling andreheating via the intermediate storage of the base compound is avoided,it is however disadvantageous, as with all other methods andarrangements according to the state of the art, that a continuousproduction of rubber end compounds is not possible. In addition, thecapability of cooling the second closed mixer operating as a finishmixer is poor as before because of its comparatively poor ratio ofcoolable surface to the quantity being mixed disposed in the mixer.

As an alternative to the closed mixer, in actual practice no alternativecould prevail for overwhelming technical reasons such as inadequatemixing capacity or thermal problems. The state of the art of producingrubber compounds is as before the closed mixer developed on the basis ofa dough masticating machine.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method and anarrangement with which a rubber end compound is produced economically inone operating step starting with crude rubber without intermediatelystoring the rubber for cooling and for diffusion substance exchange. Itis another object of the invention to provide such a method andarrangement wherein there is no vulcanization of the rubber in themixing apparatus.

With the production method made available by the invention as well aswith the production arrangement according to the invention, substantialadvantages are obtained with respect to the closed mixers primarily usedpreviously. In addition to the improvement of the quality of the endcompound producible continuously, significant savings result in theproduction costs which is made evident with respect to an example.

The closed mixers conventional today are mostly built in sizes of 50 to500 liter mixing chamber volumes. A machine size used very often in allcomponent areas of the rubber processing industry is the 350 liter mixerfor which the following comparison economic evaluation is carried out.

The cost for the production of 1 kg of vulcanizable rubber compounds ison average as follows:

    ______________________________________                                        cost of material       85%                                                    wage-dependent manufacturing costs                                                                   8%                                                     machine-dependent manufacturing costs                                                                7%                                                                            100%                                                   ______________________________________                                    

For the production costs a maximum of savings potential of 15% results.

In Table 1, the individual positions, from which the production costsare assembled, are listed, for the conventional method with closedmixers and for the newly developed method. The cost for the closed mixerprocess constitutes reliable experience values of the rubber processingindustry. The costs for the new development of the assignee herein areconservatively estimated on the basis of long years of experience withextrusion equipment. This cost comparison includes the followingindividual assumptions or experience values:

                  TABLE 1                                                         ______________________________________                                        Cost Breakdown for the Production of Rubber Compounds                                   Closed Mixer                                                                  Base    End       Method according                                            Compound                                                                              Compound  to Invention                                                DM/ton  DM/ton    DM/ton                                            ______________________________________                                        Wage-Dependent                                                                            33.70     33.70     22.50                                         Manufacturing                                                                 Costs                                                                         Machine-Dependent                                                             Manufacturing                                                                 Costs:                                                                        Electrical  37.20     13.70     59.20                                         Energy                                                                        Cooling      3.70      3.30     5.                                            Maintenance 25.80     22.90                                                   Fixed Costs 51.90     51.90     42.40                                         Costs for                                                                     Ancillary Tasks:                                                              Weighing and                                                                              26.10     12.40     26.10                                         controlling                                                                   chemicals                                                                     Transport and                                                                             23.90     24.40     --                                            Storage                                                                       Clearing Compound                                                                         --        27.50     --                                            Waste       1.        1.        1.                                            Total Costs 203.30    190.80    156.20                                                  394.10                                                              ______________________________________                                    

With a closed mixer having a size of 350 liters, approximately 2,300kg/h can be produced with conventional values of mixing time, charginglevel and preparation time in the three-shift operation. The costbreakdown is referenced to this throughput.

The compound as a rule is produced in two stages in the production withclosed mixers. In the first stage, the base compound is produced and inthe second stage, the end compound is produced. For this purpose, twocomplete machine pass-throughs are required which must be operated eachwith three operators. In contrast thereto, the subject matter of theinvention requires only two operators.

The computation of the fixed costs is based on an amortization time of15 years and an interest rate of 6%. The sum invested is composed of thecosts for the metering equipment and charging equipment, the mixingequipment including drive and control and for a batch-off unit. In thecase of an initial installation, additional costs occur for aprecomminution of the crude rubber generally delivered in the form oflumps as well as a safety surcharge of 20% for the additional costswhich cannot be estimated at the present time.

The most disadvantageous case is assumed for the installation of alaboratory unit in that several compound constituents cannot beindividually metered continuously because concentrations are too low.For producing a premixture of these compound constituents, the costs areinserted in the position "weighing and controlling of chemicals" in theorder of magnitude usual for the closed mixer process. The costs fortransport, storage and compound clearance are in contrast unnecessarysince the compound produced with the suggested arrangement is directlyfurther processed to the end product.

This cost overview is deliberately carried out with the most unfavorableassumptions and provides a reduction of the production costs of 60.4%for the method according to the invention. In 1988, a total of 2.83million tons of rubber compounds were produced in Europe with an averageprice of 8,000.00 DM/t. With a share of 15% production costs, theinvention makes a savings possible within this reference frame of DM2,051,184,000.00 alone for the European rubber industry. This means aconsiderable improvement in competitive capability by using the subjectmatter of the invention suggested here.

From the continuous operation of the production arrangement drivenaccording to the method of the invention, not only economic advantagesresult but also technical advantages. For each compounding cycle,thermal start-up effects occur in the present day conventional closedmixers as a consequence of the intermittent operation. The process isonly quasi steady state. In a continuous process as it is suggestedhere, the danger of fluctuations in quality is reduced by a multiple.

The geometry of a closed mixer is not changeable or changeable only atrelatively high cost. With the modular configuration of the productionarrangement according to the invention, the geometry of the compoundingand conveying elements can be optimally matched to the rubber compoundto be produced from which an optimal compound quality results. The costintensive clearance tests (see Table 1) are unnecessary because of thevery good quality of the compound and its time-dependent consistency. Inaddition, it is no longer necessary for many rubber compounds tointermediately store the same for the purpose of diffuse compensatingoperations. The material can be further processed to a semifinishedproduct or to an end product directly after the mixing process withoutrenewed plasticating.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained with reference to the drawings,wherein:

FIG. 1 is a longitudinal section view taken through a twin-screwextruder having main process zones A and B for the continuous productionof the rubber base compound and for the rubber end compound in oneoperation;

FIG. 2 is a longitudinal section view taken through two twin-screwextruders (D, E) in which the rubber base compound and the end compoundare separately but continuously producible;

FIG. 3 is a longitudinal section view taken through a twin-screwextruder wherein two screw pairs are mounted which are drivenindependently of each other; and,

FIG. 4 is a section view taken along line Z--Z of FIG. 1 through theextruder housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The method according to the invention can be carried out for examplewith an arrangement according to FIG. 1 with the arrangement including atwin-screw extruder. The extruder housing 1 is assembled from housingsections (aa) to (ai) connected with each other in a row and has: acharging opening 5 for the crude rubber, a plurality of additionalcharging and devolatilizing openings 22 to 26 as well as an extrudernozzle 3 at its downstream end through which the rubber end compoundleaves the extruder.

In the extruder housing 1, two intermeshing extruder screws 2 (FIG. 4)rotate which have different tasks in the different housing sections. Incorrespondence to these tasks, the extruder screws 2 have the same screwgeometries with respect to each other but with these screw geometriesbeing different in the conveying direction (for example, masticating,shearing, mixing, throttling, conveying geometries).

In the following, the production of a rubber end compound is describedto make clear the operation of such an extruder.

The extruder is subdivided into two main process zones (A, B) in whichthe production of the rubber base compound (zone A) and the productionof the rubber end compound (zone B) take place continuously. For thispurpose, crude rubber (a) is supplied continuously to the extruderthrough the feed opening 5. The extruder screws 2, configured forconveying in this extruder region, receive the crude rubber and build upa conveying pressure. In the region of housing sections (ab, ac), thecrude rubber is plasticated and homogenized and provided with chemicalsas well as a softener (b) which are fed into the extruder through thehousing opening 22.

These additives are then mixed with the crude rubber and prepared to ahomogeneous compound.

Thereafter, soot or talcum (c) is fed into the extruder through thehousing opening 23 in the housing section (ad) as further non-reactivecompound component. These additives are processed via the extruderscrews with the extrudate to a homogeneous rubber compound.

The extruder temperature increases from approximately 25° C. of thecrude rubber to 150° C. to 160° C. in the extruder section (ae) withinthis main processing zone A of the extruder. In this zone A of theextruder, only the non-reactive mixture components are fed into theextruder and a twin-screw extruder having a self-cleaning capability isused. For this reason, neither vulcanization effects nor deposits ofextrudate occur here.

In the main method zone B starting with the housing section (af), theextrudate is cooled to a temperature in the range of 100° C. to 120° C.by means of a cooling arrangement for the extruder housing. Thistemperature reduction is necessary since in this zone B of the extruder,the rubber end compound is produced by mixing in the reactive mixtureconstituents. Exceeding this temperature range would bring about anundesired premature vulcanization of the rubber compound.

The cooling of the extrudate takes place in this embodiment by means ofa liquid cooling medium, for example, water, which is conducted throughbores 4 in the extruder housing 1. A heat exchanger connected to theextruder but not shown takes care of the dissipation of the excessamount of heat from the cooling liquid.

As a departure from this embodiment, the cooling of the extruder housingcan however also take place via cooling channels provided around thehousing outer wall although a cooling via the extruder screws is alsoconceivable. In addition, another heat exchanger liquid can be used independence upon the quantity of heat to be transferred which can bestill free flowing even at initial temperatures of below 0° C.

The rubber base compound (g) which has reached the main process zone Bis then cooled in housing section (af) and, according to FIG. 1,liberated from gaseous extrudate constituents (d) via a devolatilizingopening 24. In the housing section (ag), the reactive compoundconstituents (e) such as sulfur and reaction accelerators are suppliedto the rubber compound via the feed opening 25. Thereafter, theextrudate, while being continuously cooled, is mixed with theseadditives and processed to a homogeneous rubber compound. In theextruder region formed by the housing section (ah), the extrudate isliberated once more from its volatile constituents (f) via the housingopening 26 in order, finally, in the region of the housing section (ai),to be brought to the necessary pressure by the extruder screws 2. Theextrudate leaves the twin-screw extruder finally via the extrusionnozzle 3 as rubber end compound which is so well homogenized that nofurther intermediate storage is necessary for the random materialtransfer which was conventional up to now and therefore can betransported away directly for continuous further processing.

A variation of the arrangement according to the invention is shown inFIG. 2. In this embodiment, the base compound is produced in a firsttwin-screw extruder D and the end compound is produced in a secondtwin-screw extruder E. The extruders D, E are assembled in a mannercomparable to the extruder of FIG. 1; however, the main process zone Ais realized in extruder D and the main process zone B is realized inextruder E. The supply of the mixture components as well as thedevolatilizing of the extrudate takes place at the same housing openingsas in the extruder according to FIG. 1 and under the same thermalconditions. The rubber base compound (g) produced in the extruder D isfed directly into the feed opening 6 for the base compound in theextruder E and is there processed further to the rubber end compound.

Compared to the state of the art, in this embodiment of the arrangementof the invention, the base compound also does not have to beintermediately stored for cooling down and thereafter brought to arequired temperature level in a second mixing arrangement with thetemperature level being necessary for mixing in the reactive mixturecomponents.

In still another embodiment, the arrangement is formed by a twin-screwextruder according to FIG. 3 for carrying out the method of theinvention. This extruder has two screw pairs 12, 13 which are driven atmutually opposite ends of the extruder housing 9, 10 by drive units 7,8. The extruder housing is here also subdivided into two main methodzones A, B which can be determined by the length of the extruder screwsand/or by the extruder housing sections provided with or without coolingchannels 11. The screws 13 of zone B have a greater diameter than thescrews 12 of zone A and the inner diameters of the housing regions 9, 10are configured in the same or similar ratio to each other.

The crude rubber (a) is filled into the extruder via an inlet opening 16where the crude rubber is homogenized and plasticized in the region ofthe main method zone A and provided with the non-reactive mixturecomponents (b, c) necessary for producing the rubber base compound. Inthe method zone B, the extrudate is devolatilized (d, f) and providedwith the reactive mixture constituents (e). The compounding constituents(e) are mixed with continuous cooling into the base compound andprocessed with the base compound at a temperature of 100° C. to 120° C.to a homogeneous end compound. Finally, the end compound leaves themixing arrangement via the extruder outlet opening 15.

The rubber compound produced at a laboratory scale with the method ofthe invention in an embodiment of the arrangement of the inventionaccording to FIG. 1 was excellent notwithstanding previous skepticism.This was that much more surprising because skilled persons in this areaof technology were burdened for decades with the disadvantages of theclosed mixers and a use of the twin-screw extruder for continuouslyproducing rubber end compounds was not previously discussed.

The quality of the end compound obtained can be judged with respect toexperimental examples.

    ______________________________________                                        Formulation A (Passenger Car Tire Tread)                                      Mixing Components                                                                             Percentage by Weight                                          ______________________________________                                        rubber SBR 1712 58.0                                                          soot N 339      31.6                                                          aromatic oil    6.3                                                           antiaging agent IPPD                                                                          0.6                                                           stearic acid    0.8                                                           zinc oxide      1.3                                                           sulfur          0.6                                                           accelerator VDM/C                                                                             0.5                                                           accelerator VD/C                                                                              0.3                                                                           100.0                                                         ______________________________________                                    

The rubber utilized in this mixing experiment had a feed temperature of25° C. and the temperature of the extrudate in the extruder section (ae)was 160° C. Ahead of the inlet opening 25 for the reactive mixingcomponents, an entrudate temperature of 105° C. was measured which couldbe maintained along the entire main method zone with deviations of ±5°C. The temperature of the extrudate just ahead of the extruder nozzlewas determined to be 115° C. For a screw diameter of 90 mm, the methodzone A+18 (screw diameter) and in the method zone B was likewise +18(screw diameter). Approximately 500 to 600 kg of end compound per hourwere produced with the arrangement described. The end compound was of avery good homogeneity and had a significantly better degree of sootdispersion compared to compounds produced in closed mixers. Thescattering of the rheometer curves for investigating the vulcanizationperformance of the compounds also showed a significantly better resultin comparison.

For the same extruder dimensions and temperature levels, approximately500 kg of end compound per hour were produced in an experiment forproducing an end compound for truck tire treads pursuant to formulationB. In principle, the same comparison results were obtained.

    ______________________________________                                        Formulation B (Truck Tire Tread)                                              Mixing Components  Percentage of Weight                                       ______________________________________                                        natural rubber RSS3                                                                              60.5                                                       soot N 220         30.2                                                       aromatic oil       1.8                                                        antiaging agent IPPD                                                                             0.6                                                        antiaging agent TMQ                                                                              0.6                                                        wax for protection against light                                                                 0.9                                                        stearic acid       1.8                                                        zinc oxide         1.8                                                        accelerator MBS    0.9                                                        sulfur             0.9                                                                           100.0                                                      ______________________________________                                    

In a third experiment, the end compound for automotive profilesaccording to formulation C was produced according to the method of theinvention. Here too, the temperatures are maintained at the levelmentioned above and 400 kg per hour were produced. The quality of theend compound was excellent also in this experiment.

    ______________________________________                                        Formulation C (Automotive Profile)                                            Mixing Components                                                                              Percentage of Weight                                         ______________________________________                                        rubber EPDM      23.0                                                         zinc oxide       1.2                                                          stearic acid     0.2                                                          soot N 550       29.0                                                         chalk            18.7                                                         naphthene base petroleum                                                                       26.5                                                         accelerator TP/S 0.7                                                          accelerator TMTD 0.3                                                          accelerator MBT  0.2                                                          sulfur           0.2                                                                           100.0                                                        ______________________________________                                    

It is understood that the foregoing description is that of the preferredembodiments of the invention and that various changes and modificationsmay be made thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. A method for continuously producing a a rubberend product in a single stage from crude rubber, the method comprisingthe steps of:feeding the crude rubber (a) into a two-screw extruderhaving a predetermined length and intermeshing self-cleaning extruderscrews wherein the crude rubber is plasticized; feeding non-reactivemixing additives needed for producing a base compound (g) into thetwin-screw extruder at preselected distances along the length of thetwin-screw extruder; mixing and homogenizing the non-reactive mixingadditives with the plasticizer crude rubber (a) in said extruder attemperatures in the range of 100° C. to 160° C. to form the basecompound (g) while simultaneously avoiding the formation of vulcanizedparticles and deposits of extrudate because of the intermeshingself-cleaning operation of said extruder screws; cooling the basecompound (g) down in said twin-screw extruder to a temperature in therange of 100° C. to 120° C.; adding all reactive mixing additives neededfor producing the end product to the base compound (g) while in saidtwin-screw extruder and while maintaining the base compound (g) in saidtwin-screw extruder at a temperature in said range of 100° C. to 120°C.; and, mixing and homogenizing said reactive mixing additives intosaid base compound (g) in said twin-screw extruder while continuouslycooling said base compound to maintain the temperature thereof withinsaid range of 100° C. to 120° C. thereby preventing vulcanization andproducing the rubber end product.
 2. A method for continuously producinga rubber end product in a single stage from crude rubber, the methodcomprising the steps of:subdividing a twin-screw extruder having apredetermined length and intermeshing self-cleaning extruder screws intoa first process zone for producing a base compound from the crude rubberand a second process zone for producing the rubber end product from saidrubber base compound; feeding crude rubber into a feed opening of saidtwin-screw extruder in said first process zone wherein the crude rubberis plasticized; feeding non-reactive mixing additives needed forproducing the base compound into the twin-screw extruder at preselecteddistances along the length of the twin-screw extruder within said firstprocess zone; mixing and homogenizing the non-reactive mixing additiveswith the plasticized crude rubber in said twin-screw extruder in saidfirst process zone while increasing the temperature of said crude rubberinto the range of 100° C. to 160° C. to form the base compound whilesimultaneously avoiding the formation of vulcanized particles anddeposits of extrudate because of the intermeshing self-cleaningoperation of said extruder screws; passing said base compound to saidsecond process zone and cooling the base compound down in saidtwin-screw extruder to a temperature in the range of 100° C. to 120° C.and allowing gaseous extrudate constituents to escape from said basecompound through a first devolatizing opening of said twin-screwextruder in said second process zone; adding reactive mixing additivesneeded for producing the end product to the base compound through a feedopening of said twin-screw extruder in said second process zone whilemaintaining the base compound in said twin-screw extruder at atemperature in said range of 100° C. to 120° C.; mixing and homogenizingsaid reactive mixing additives into said base compound in saidtwin-screw extruder while continuously cooling said base compound tomaintain the temperature thereof within said range of 100° C. to 120° C.thereby preventing vulcanization and producing the rubber end product;allowing volatile constituents to escape from the end product through asecond devolatizing opening of said twin-screw extruder in said secondprocess zone downstream of said first devolatizing opening; and, passingsaid end product from said twin-screw extruder.
 3. A method forcontinuously producing a rubber end product in a single stage from cruderubber, the method comprising the steps of:providing first and secondtwin-screw extruders each having a predetermined length and intermeshingself-cleaning extruder screws; assigning said first twin-screw extruderto a first process zone for producing a base compound from crude rubberand assigning said second twin-screw extruder to a second process zonefor producing the rubber end product from said rubber base compound;feeding crude rubber into a feed opening of said twin-screw extruder ofsaid first process zone wherein the crude rubber is plasticized; feedingnon-reactive mixing additives needed for producing the base compoundinto said first twin-screw extruder at preselected distances along thelength thereof within said first process zone; mixing and homogenizingthe non-reactive mixing additives with the plasticized crude rubber insaid first twin-screw extruder while increasing the temperature of saidcrude rubber into the range of 100° C. to 160° C. to form the basecompound while simultaneously avoiding the formation of vulcanizedparticles and deposits of extrudate because of the intermeshingself-cleaning operation of the extruder screws of said first twin-screwextruder; passing said base compound to said second process zone andcooling the base compound down in said second twin-screw extruder to atemperature in the range of 100° C. to 120° C. and allowing gaseousextrudate constituents to escape from said base compound through a firstdevolatizing opening of said second twin-screw extruder; adding reactivemixing additives needed for producing the end product to the basecompound through a feed opening of said second twin-screw extruder whilemaintaining the base compound in said second twin-screw extruder at atemperature in said range of 100° C. to 120° C.; mixing and homogenizingsaid reactive mixing additives into said base compound in said secondtwin-screw extruder while continuously cooling said base compound tomaintain the temperature thereof within said range of 100° C. to 120° C.thereby preventing vulcanization and producing the rubber end product;allowing volatile constituents to escape from the end product through asecond devolatizing opening of said second twin-screw extruderdownstream of said first devolatizing opening thereof; and, passing saidend product from said second twin-screw extruder.